L-glutamic acid is a representative amino acid produced by fermentation. The annual worldwide production of L-glutamic acid is estimated to be more than one million tons, which is comparable to compounds commonly used in the chemical industry. L-glutamic acid has been widely used in pharmaceuticals, food, animal feedstuffs, and other products.
L-glutamic acid has conventionally been produced by fermentation mainly using so-called coryneform L-glutamic acid-producing bacteria belonging to the genus Brevibacterium, Corynebacterium or Microbacterium, or variants thereof (“Amino Acid Fermentation”, Gakkai Shuppan Center, pp. 195-215, 1986). Production of L-glutamic acid by fermentation using other strains includes methods using a microorganism belonging to the genus Bacillus, Streptomyces or Penicillium (U.S. Pat. No. 3,220,929); a microorganism belonging to the genus Pseudomonas, Arthrobacter, Serratia or Candida (U.S. Pat. No. 3,563,857); a microorganism such as a bacterium belonging to the genus Bacillus, Pseudomonas, Serratia, or Aerobacter aerogenes (currently Enterobacter aerogenes) (Examined Japanese Patent Publication (KOKOKU) No. 32-9393 (1957)); and a mutant strain of Escherichia coli (Japanese Patent Laid-open Application (KOKAI) No. 5-244970 (1993)).
Many studies have been conducted to improve the productivity of L-glutamic acid by changing the medium composition and developing a resistance strain. For example, a strain having resistance to β-fluoropyruvate was developed in order to increase the supply of pyruvate, which is used as an intermediate in the glutamic acid-producing metabolic pathway.
The productivity of L-glutamic acid has been considerably improved through the aforementioned methods. However, to meet increasing demand in the future, a less expensive and more effective process for producing L-glutamic acid needs to be developed.
In this regard, the inventors of this application conducted intensive and thorough research into the development of a bacterial strain producing L-glutamic acid at higher yields. The research resulted in the finding that, when cg2624 and cg2115 genes are knocked out, so that they are not expressed, the knock-out mutant has increased glycerol utilization and produces higher concentrations of L-glutamic acid even with lower biomass compared to a parental strain having an ability to produce L-glutamic acid, thereby leading to the present invention.